1. Field of the Invention
The present invention relates to an improvement in the structure of the insert part of an endoscope.
2. Description of the Related Art
The insert part of an endoscope that comprises a flexible tube and a distal end part connected to the distal end of the flexible tube must be as thin as possible in order to minimize the pain inflicted on the patient. In the present level of art, however, it is difficult to form a solid-state image pickup device, for example, a charge-coupled device (CCD), as thin as an image guide fiber bundle. In consequence, the distal end part that incorporates such a solid-state image pickup device is unavoidably thick to a certain extent.
If the flexible tube is formed thick in conformity with the distal end part, the pain inflicted to the patient increases. Since the signal cable of the solid-state image pickup device is not very thick, if the flexible tube is made thick, a useless space will be produced inside the tube.
Therefore, in the insert part of an endoscope that incorporates a solid-state image pickup device in the distal end portion thereof, it is preferable to form only the distal end part thick in comparison with the flexible tube, and the distal end part is commonly formed with a circular cross-sectional configuration.
However, the distal end part having a circular cross-sectional configuration becomes exceedingly thick when incorporating a solid-state image pickup device, so that great pain is inflicted on the patient when the distal end part passes through the patient's throat, for example. When the insert part is inserted into a bronchial tube, the distal end part clogs it and obstructs passage of air to the inner part of the bronchial tube.